When you run smbd -V on your Snow Leopard installation, you'll see it's running SAMBA version 3.0.28a-apple. While I'm not sure how much difference the "-apple" makes, version 3.0.28a is old. Very old. In other words, it's riddled with bugs. Apple hasn't updated SAMBA in 3 years, and for Lion, they're dumping it altogether for something homegrown. The reason? SAMBA is now GPLv3.

Under other circumstances that could be true, but in this case apple stopped updates only since Samba went to GPL3. If the reason was technical, there would be no reason for apple to discontinue updates while their in house version was in development. Therefore, we can be fairly certain the GPL switch was the cause.

True but it depends on how they actually implement the integration between the Finder and SAMBA given that SAMBA is licensed under GPL and the said libraries cannot be linked directly to - unless of course the SAMBA libraries are licensed under LGPL. It all comes down to, I guess what the situation is behind the scenes - I'm sure there is a logical reason for it but unless they come forward and explain it in detail I see all explanations so far as being mere rectum plucking (along with my own take on the matter).